Chile, since 1991, has seen an increase of notified cases of HIV/ AIDS among certain regions of the country. The Chilean government offers free screening for HIV using only the ELISA test. In addition, many Chileans fail to return to receive their test results, as do many other individuals worldwide. In the United States, the Center for Disease Control reported that when using the "gold standard of HIV testing" (the ELISA) 30% of people with negative results and 39% of people with positive results do not return for their test results.